87yo_ta

Here I go again, two times in the last several months I'm having electrical issues and I SUCK at electrical. Alternator not charging when I put the meter on the battery terminals while running. In the past the brake and battery/charge lights came on indicating a bad alternator. This time I get NO battery light period. When I turn the key I get oil, brake and seat belt lights but no battery/charge light. I checked all the fuses I can find, both inside at the fuse box and at the fuse box in the engine compartment, and all look fine. Any ideas before I rip the alternator out and have it checked? Having no battery/charge light at all has me thinking it's something else. UGH!!
Thanks

old87yota

I am getting better at the electrical stuff but still have more to learn.

What is the year and model of your truck?

How can you tell that the alternator is not working?

Running voltage should be in the 13-14 V range.

First off, take a look at the battery. How old is the battery? Do you get 12.6 volts when the truck is not running?

Don't forget to check for corrosion around the battery terminals and electrical connections. All sorts of problems can be solved by cleaning connections and making sure they have good contact and are tight.

Since the charge light does not light up when you first turn the key, I would check to see if the bulb in the cluster has burned out. With the age and millage of these trucks, that is definitely a possibility.

wyoming9

iTrader: (1)

Bulb burnt out ??

87yo_ta

1987 4WD Pickup 22R. The voltage reading was 9.6v when checked with the meter at the battery while running. 12.4v after I put a charger on the battery. Terminals look good. I'll try to trace the wires from the alternator to the battery and check connections. Not sure about the bulb itself but will try to figure out how to get to it.

ewong

if low voltage at battery when running - I suspect a "bad cell" in the battey

http://electronics.stackexchange.com...are-the-implic

scope103

9.6v? That wouldn't be enough to start the vehicle. Did you jump it to start it? If so, ewong may be correct. You may need to load test the battery.

Visually inspect the 3-conductor plug to the alternator. The "alt" light on the dash illuminates when the IGN fuse powers it (key-on) through a ground on the yellow wire through the alternator (the light extinguishes when the alternator produces enough voltage, so that the "alt" light has 12v on each side.) If that wire is not connected, the light won't do anything. If any of the other wires are disconnected, the altenator won't produce power.

Around here, auto supply shops will load test a battery and function test an alternator for free. Before you tear the combination meter apart to check the bulb, I think I'd pull the battery and alternator and run them down for a test.

4RunnerFreak12

Does it drive? Why remove alt and batt to test most places can test with them IN the vehicle.

Sounds like bad cell in battery due to voltage issues and burnt bulb since it's not coming on (or a short?)

Def check wires that go from alt to batt

Good luck electrical is a nightmare! I would rather replace a clutch lol

87yo_ta

Yes, I jumped started it. I put a battery charger on it later and after two days it still reads 12.6 volts. After charging it the truck starts easily but the voltage drops instead of showing that it is being charged. If the alternator was not charging, and the battery was low due to running the vehicle without knowing the alternator was dead, wouldn't no charge at all while running indicate a bad alternator?
And yes, I'll replace the clutch any day before I'll tackle electrical!

scope103

The reason I hesitate on the "bad alternator" diagnosis is the lack of an "alt" light. Generally, a bad alternator will still light the "alt" light. You could have a burnt-out bulb and a bad alternator at the same time -- a sad coincidence. But a disconnected (broken) alternator plug would do both.

Since you already have the tools, an easy test would be to look at the voltage on the "B" terminal of the alternator -- the single fat wire connected with a big copper nut. It should be at 13.9-15.1v (but temperature dependent http://web.archive.org/web/201102051.../2onvehicl.pdf), and it should be the same voltage as right on the battery. If that voltage is okay but the battery is at 12.6v and falling, you have a bad fat wire connection. But it doesn't explain the lack of "alt" light.

When you change a clutch, a goof could drop a 50-lb transmission on your head. With electrical, a goof could drop a 12 ounce multimeter on your foot. Your choice.

Charchee

Need to load test that battery. A local parts store can do it either on or off the vehicle. It's best to have it charged when you do it. It sounds like you may have replaced the alternator at some point. Is that true? A bad alternator can damage a battery internally to the point that it will show good voltage but have a bad cell that causes it to drain almost instantly whenever it has a load on it. Other things besides alternators can cause this of course and a battery can just go bad over time as well. Don't let a battery with good voltage fool you. I've been troubleshooting electrical systems for over a decade and they still fool me from time to time. You can even load test it yourself. With a fully charged battery, have somebody crank the truck while you are measuring voltage at the battery and see what happens. I've seen them fall to that 9V range and I've even seen one short out and show a negative voltage once. You should see it pull down and almost instantly pull back up to at least 13V. If it won't crank and the voltage falls to like 3V, replace that battery.

Don't pull your alternator out. You can easily test it with a voltage meter just like you are testing it at the battery. If your battery tests good and your alternator tests good then look at the wiring between them for your issue. It's not going to be a big deal so don't pull out the wrenches just yet. Just see if you can get a load test on that battery before you go any further.

87yo_ta

Well, I"m not sure who the winner is here besides me because my truck is fixed. I took everyone's advice. I checked wires, plugs and fuses. Had the battery load tested and the alternator tested. Battery was fine but the alternator failed so I bought a new alternator and figured I'd tackle the battery light issue later. Turns out once I installed the alternator the charge/battery light began working again! Guess the alternator CAN wreak havoc on the charge light so need to add that to the online service manual. :-) Thanks to everyone for chipping in and offering their advice!

Charchee

Good deal. I bet your alternator shorted out internally and burnt the connection to the charging system light. I sure would have thought the light's power during the test flash would have come from the dash power so you would know it was functional even with a total alternator failure but it may actually be fed exclusively from the alternator terminal. This one is going in my notes.